1. Field of the Invention
This invention relates to a magnetic recording medium, such as magnetic tape and, more particularly, to an improvement in a back coating layer provided to the reverse side of the substrate with respect to the magnetic layer for prevention of loose winding or electrostatic charging.
2. Description of the Prior Art
In preparing a magnetic recording medium in general, a magnetic paint formed by dispersing and kneading ferromagnetic particles, binder, dispersant and lubricant in an organic solvent is coated on a non-magnetizable substrate such as polyester film and dried to a magnetic layer.
When desired to improve the properties of the magnetic recording medium such as magnetic tape used in a VTR for providing a higher image quality, it is necessary to reduce the particle size of the ferromagnetic particles contained in the magnetic layer and to elevate packing density while elaborating the surface of the magnetic layer to a smooth finish so as to provide for a more intimate contact between the magnetic layer and the magnetic head. For realizing a smoother surface of the magnetic layer, it is also essential to improve smoothness of the surface of the non-magnetizable substrate.
However, when surface smoothness of the magnetic layer and/or the substrate is elevated in this manner, the magnetic recording medium is likely to be tightly affixed to, for example, the guide member of a magnetic recording and/or reproducing device, when the magnetic recording medium is a magnetic tape. This gives rise to increased friction and deteriorated running characteristics. Moreover, there may occur powder debris or wear of the substrate. In addition, a so-called air film may be formed between the adjacent tape turns with resultant loose winding.
In order to overcome such deficiency, it has also been customary to provide a back coating layer on the opposite side of the non-magnetizable substrate with respect to the magnetic layer.
However, the conventional back coating layer is not entirely satisfactory especially with respect to running durability and surface roughness of the back coating layer itself, thus occasionally causing deterioration in an S/N ratio, increase in dropouts. In addition, wear or powder debris may be caused to the back coating layer, the back coating layer may be bonded to the magnetic layer or loose winding may be caused. Up to now, there exists no back coating layer capable of tolerably satisfying the various criteria demanded of the back coating layer.